Cal. Food & Agr. Code § 16908
It is unlawful for any person that owns or operates any motor truck, or motor truck and trailer, or semitrailer, to confine or permit to be confined, in such vehicle, any animal for a longer period than 28 consecutive hours from the time the animal was last fed and watered. Upon the written request of the owner or person in charge of the animal, the period of confinement may be extended to 36 hours. Before the expiration of the permissible period of confinement, the animal shall be unloaded in a humane manner by means of a chute or tailgate of sufficient size into properly equipped pens for rest, water, and feeding, for a period of at least five consecutive hours.
The failure of a person to feed or water an animal within the time limit prescribed by this section is not a violation of this section if the feeding and watering of the animal is prevented by storm or other accidental or unavoidable causes which could not be anticipated or avoided by the exercise of due diligence and foresight.
Ca. Food and Agric. Code § 16908